Sustainable green neem oil–based polymeric and Nanocrystalline cellulose additives: Synthesis, characterization, and performance in lubricating oils

There has been significant interest in the use of green additives produced from bio-based materials within the lubricant industry. These additives are characterized by their non-toxic nature, cost-effectiveness, natural biodegradability, and diverse applications. The current study focuses on the synthesis of a Neem oil-derived homo-polymer, as well as a copolymer formed from Neem oil with Nanocrystalline cellulose (NCC). GC-MS analysis identified the fatty acid composition of neem oil, which was primarily dominated by the presence of oleic acid (∼19 %), which offers crucial reactive sites for the process of free-radical polymerization. This led to the formation of both homo-polymers and copolymers. Following this, FTIR confirmed the formation of both copolymer and homopolymer due to the absence of the olefinic peaks in the 1550–1680 cm⁻¹ region as opposed to their presence in the neat neem oil. The successful isolation of nanocrystalline cellulose (NCC) was validated through FTIR, which indicates a complete removal of the characteristic lignin peak around 1500–1600 cm⁻¹ and the hemicellulose carbonyl peak near 1735 cm⁻¹, both of which are observable in the raw husk. The TGA analysis demonstrated the enhanced thermal stability of the copolymer, with about 5 % weight loss at 300°C in contrast to a 15 % loss for the homopolymer at the same temperature. The pour point and Viscosity Index of the base oil were analysed before and after the addition of the synthesized additives at different concentrations. Specifically, the polymers (both homo-polymer and copolymer) were evaluated at concentrations of 1 %, 2 %, and 3 % (w/v), whereas the NCC was assessed at 1 % and 2 % (w/v). The base oil containing 2 % copolymer was found to be optimal, yielding the highest Viscosity Index of 111.1 and a notably lower pour point of −14°C. These results confirmed the efficiency and applicability of synthesized NCC, a homo-polymer of neem oil, and copolymer as additives for lubricating oil to improve, specifically, its pour point and Viscosity Index.